1. Field of the Invention
This invention relates to a rock stabilizing apparatus for anchoring unstable rock formations in underground mines and construction sites and more particularly relates to an apparatus and method that concurrently employs both chemical and mechanical anchor means to anchor a rock bolt within an unstable rock formation.
2. Background of the Invention
It is well known in mining and construction operations to reinforce roofs, sides and floors of tunnels and shafts using rock bolting. The rock bolts are inserted into a drilled hole and are anchored in place chemically by either a quick curing resin-based adhesive material or mechanically by such devices as expanding anchors adapted to frictionally engage the wall of a drilled hole. Examples of both methods are found in U.S. Pat. Nos. 6,146,055, 6,698,980 5,344,257 and 5,219,248.
Using a concurrent combination of mechanical and chemical anchors to anchor a rock bolt in a drilled hole is also known in the art and has the combined advantages associated with each individual method. One such device is described in U.S. Pat. No. 5,222,835 “Resin-Mixing Article for Mine Roof Anchor” issued to Wright on Jun. 29, 1993. However, Wright does not teach an integrated chemical-mechanical anchor, but rather describes a device where the resin package is placed in the drilled hole in advance of the rock bolt and then the rock bolt is inserted to pierce the package and permit the resin to flow around a portion of the rock bolt. Mechanical anchoring means in the form of a conventional expanding anchor assembly is then used to anchor the rock bolt. The Wright invention discloses a number of weaknesses in combined chemical-mechanical rock bolt anchoring systems. First of all, the Wright invention does not keep the resin material within a predefined portion of the annulus between the rock bolt and the wall of the drilled hole. The resin is permitted to flow around the rock bolt in an uncontrolled manner and back down the drilled hole until such a time as the resin has sufficiently cured to prevent flow. This can have the result of creating voids within the resin material and wasting resin adhesive that may flow down the drilled hole and merely coat the wall of the drilled hole rather than anchor the rock bolt to the wall of the drilled hole. The effect is that the total adhesive capability of the resin is not achieved. Secondly, the resin package is inserted into the drilled hole in advance of the rock bolt. This means that the resin package could be damaged during insertion and tamping to the top of the hole. Resin leakage will again result in the reduction of resin adhesive capability.
Therefore there is a requirement to provide an apparatus that integrates both chemical and mechanical bonding means into rock bolt anchor, takes full advantage of the total adhesive capabilities of the adhesive material and protects the resin package from damage before it needs to be ruptured. There is also a further need to provide for a mechanical anchoring means that can be adapted with an integral chemical anchoring means for use in fragmented rock formations.